I did I a quick search and they have a guide to replacing the hard drive. In the comments, there are lots of recommendations fir hard drives that work. The largest I saw listed on there was 6 GB.
I just installed a regular off the shelf hard drive (I formatted it to HFS like the original one was), reset the Time Capsule and it took care of formatting and everything.
I just installed a regular off the shelf hard drive (I formatted it to HFS like the original one was), reset the Time Capsule and it took care of formatting and everything.